We are continuing our studies on biotin in laboratory animals using the intact rat or chick as well as various tissue preparations at the organ, cellular and subcellular level. The biotin-deficient animal is used as a tool to study 1) the metabolic regulation of gluconeogenesis and 2) the synthesis of biotin holoenzymes such as pyruvate carboxylase, propionyl CoA coarboxylase and acetyl CoA carboxylase from their apoproteins and biotin. BIBLIOGRAPHIC REFERENCES: In vitro synthesis of pyruvate holocarboxylase in rat liver and kidney, by S.P. Mistry and Grace Shen Chiang. Federation Proceedings, 34:942 (1975); Changes in the concentrations of some metabolites in rat kidney under different nutritional states, by P.N. Achuta Murthy and S.P. Mistry. Federation Proceedings, 35:684 (1976).